I own a pair of 3A sigs and have two friends with RM40's and have heard RM40's on numerous occasions and am very familiar with how they sound.
rblnr is correct in that the Vandersteens are not as dynamic as the VMPS and present a more laid back sound.
Imaging:
IMO the 3A's image significantly better than the RM40's, some of that may be the room but I've heard the 40's in 4 different rooms and I believe the 3A's disappear sonically better than the 40's do.
Dynamics:
No question the 40's are a more dynamic speaker. They will go from a whisper to a shout very quickly and can provide a great deal of impact. They will also play quite a bit louder than the 3A's but it sounds like you like to listen at lower levels so this may not matter as much.
Bass:
The 3A's have tuneful, articulate and fairly extended bass. The 40's also have excellent bass which is easily tunable via the PR. I believe the 40's have more bass slam and punch. I am quite happy with the bass on the 3A's but some folks will certainly want more.
Midrange:
This is the hard one to compare since the VMPS use a ribbon and the Vandersteen uses a cone driver, albiet a very unusal cone. I prefer the presentation of the 3A's to the 40's. I find the midrange on the VMPS can be a bit aggressive and forward for my tastes. Note that both of the RM40's I've heard have the lower XO point for the midrange panels, the later models will be different.
Treble:
The 3A's have a very smooth and extended treble as do the 40's. Some folks find the treble of the 3A's to sound soft. IMO this is due to the first order XO and is quite natural and unforced. I find the sound of the FST tweeter to be very smooth and detailed.
One thing I have observed is that the 3A's sound better at lower volumes than the 40's. It seems to me that the 40's don't really come alive until they have some juice running through them.
As for WAF, the Vandy's probably don't qualify as fine furniture but I have been able to get my wife to tolerate them in our living room. If I tried to bring in speakers the size of the 40's I would be laughed out the door. The RM30's would be a different story.
I don't know if this helps any but it's my $.05's worth.
One last thing, one of the RM40 owners I know had ML Prodigies prior to the 40's. I believe he likes the 40's better.
Given the amount of money you are looking to spend I would probably make the drive for an audition but that's just me.
